Avionic antennas with multiple radiating elements may be used to transmit an omnidirectional pattern or a directional pattern. The accuracy of the pattern may depend upon the accuracy of the phases of the signals driving the antenna. Conventional relatively high power avionic transmitters provide multiple output signals for driving an antenna having a plurality of elements. Such transmitters may include a plurality of similar circuits, each circuit driven from a common source and providing one of the output signals. A typical circuit may include a power amplifier followed by a phase shifter to set a desired output phase and compensate for phase differences introduced by different power amplifiers. The phase shifter necessarily operates at the relatively high power of the output signal. Such phase shifters are expensive and bulky. They consume power and consequently contribute adversely to the thermal characteristics of an enclosed transmitter.
Another conventional avionic antenna has fixed phase shift circuits integral to the antenna assembly to facilitate transmitting one of a set of directional patterns. To use this antenna to transmit omnidirectionally will require an accurate phase relationship among transmitter output signals coupled to the ports of such an antenna.
Without the present invention, further improvements cannot be made in avionic transmitters such as reducing the size, reducing power consumption, and improving phase accuracy of output signals. Improved phase accuracy contributes to improved patterns for directional and omnidirectional uses of an antenna used with the transmitter. Improved patterns are desired for improved communication such as is used for aircraft collision avoidance. Without the present invention, improved aircraft collision avoidance cannot be achieved. Consequently, the risk of loss of life and property cannot be reduced.